Mashable

Richard Vevers, the founder of the nonprofit Ocean Agency, and his partners at the XL Catlin Seaview Survey have been witnessing an ecological disaster unfolding in coral reefs worldwide since 2014.

The group’s mission is to document, in unprecedented detail, the third-ever global coral bleaching event on record, and by far the longest such event ever seen.

Using high-tech, 360-degree cameras that are also contributing to Google’s efforts to provide underwater maps of the world’s oceans, Vevers’ team has been making sure that this bleaching event does not go unnoticed by the world. On Tuesday, the Ocean Agency released its latest batch of images of coral bleaching and coral death caused by unusually warm ocean temperatures — related to both El Niño and long-term, human-caused global warming.

This time, though, the pictures were not of some remote coral atoll known only to divers, but rather the iconic Great Barrier Reef of Australia.

The images show the shocking toll that warm ocean waters have exacted on one of the world’s greatest ecological treasures.

A World Heritage site, the reef stretches for 2,300 kilometers, or 1,430 miles, from the northeastern tip of Queensland south to Townsville. During the bleaching event, ocean temperatures exceeded tolerable levels for most reef communities for at least 8 months, reaching as much as 4 degrees Celsius, or 7.2 degrees Fahrenheit, above average.

The northern part of the Great Barrier Reef was hardest hit during this event, with an estimated 35% of reefs on the northern and central parts perishing. The southern portion of the reef was not hit as hard, with less than 5% reef mortality south of Cairns, according to a scientific survey by researchers at the ARC Center of Excellence for Coral Reef Studies at the end of May.

In an email to followers of the project on Tuesday, Vevers and his team said that even with that caveat, this was a historic disaster.

Before and after image showing coral bleaching at Lizard Island on the Great Barrier Reef in March 2016, and the same reef in May 2016 after the coral had died.

A before and after image of coral bleaching and later dying in March / May 2016, at Lizard Island on the Great Barrier Reef.

The corals had lost their colour and their skeletons, visible through their clear flesh, were glowing white.

“Even the most conservative estimates of the impact in the north still rank the bleaching as one of the worst environmental disasters in Australian history,” Vevers' team stated on the Ocean Agency website. “We were there to see it first hand and it was the most disturbing sight we have ever seen.”

The team began their latest mission at Lizard Island, a national park located off the coast of northeastern Queensland. They had visited that location five weeks earlier, while it was “at the height of the bleaching.”

“On the last trip the reef at Lizard Island was in the sad but hauntingly beautiful phase — the corals had lost their colour and their skeletons, visible through their clear flesh, were glowing white,” the team wrote.

“We were expecting to see a similar but faded sight when we returned, but when we jumped in to revisit the sites we knew so well from the previous trip, we were shocked by the transformation. The white hard corals had turned brown — they were dead and covered in algae,” the team reported. “They looked like they'd been dead for years. The soft corals were even more shocking. They were in a state of decomposition and were literally dripping off the rocks.”

Coral bleaching occurs when coral expels the algae, known as zooxanthellae, that lives in its tissue, giving it color and nutrients. This action, caused by stresses such as increased water temperature and pollution, leaves the coral skeleton exposed, making it more susceptible to heat stress, disease and pollution.

Bleached corals can recover if the ocean waters cool or pollutants diminish. However, they can die if the stressors last too long.

“It was a deeply disturbing sight. It was followed by a deeply disturbing smell as soon as we got out of the water. We smelt of the rotting flesh of animals. It was an experience we will never forget," the team wrote.

“We hope we never have to witness anything like it again. But we know we will. The ocean is committed to continued warming for at least the next two decades due to carbon emissions already in the system. Dangerous climate change is here and it's now or never for protection of coral reefs.”

The oceans are absorbing the vast majority of the heat that burning fossil fuels like coal and oil is adding to the Earth’s climate. Studies show that ocean heat has been climbing rapidly in recent years, and coral reefs that cannot withstand warmer waters may have a more difficult time surviving in the future.

Other, hot-water-tolerant species may emerge as ecological winners, providing bright spots of biological diversity, but not the same bounty of marine life as exists today at reefs worldwide.

The coral bleaching event is no longer underway in Australia, but it continues elsewhere, including much of the Northwestern Pacific and the Indian Ocean, and is predicted to last at least until the end of the year.